1. Field of the Invention
The present invention relates to a power saving device in which a microcomputer is shut down in a standby state.
2. Description of the Related Art
An electronic device such as an AV device has a standby state, where power is supplied only to the microcomputer and to the peripheral circuits thereof so that the power of the device can be turned back ON in response to a user's operation of a remote control even when the power of the device is OFF. Recently, there is a demand for further reducing the standby power consumption, i.e., the amount of power to be consumed in a standby state. In view of such a demand, the microcomputer has a power saving mode in which the microcomputer itself is shut down when the microcomputer has no process to execute. Then, in response to a remote control signal, an interrupt signal is input to an interrupt terminal of the microcomputer for triggering a transition from the power saving mode to the normal mode. If the remote control signal is a signal that does not require the transition to the normal mode (e.g., a “Stop” signal of a CD player), the microcomputer transitions from the normal mode back to the power saving mode. However, whether the remote control signal does or does not require the transition to the normal mode can be determined only after receiving the remote control signal completely. With a conventional method, the microcomputer stays in the normal mode while analyzing the remote control signal. Therefore, such a conventional method fails to save the power consumption during the remote control signal receiving period.
Patent Document 1 (Japanese Laid-Open Patent Publication No. 2001-14073) discloses a device in which the microcomputer in the standby state performs an intermittent operation in which the power saving mode and the normal mode are alternated with each other until a remote control signal is received. When a remote control signal is received, the normal mode is extended (continued) to analyze the remote control signal. With this device, however, the microcomputer is in the normal mode while analyzing a remote control signal, thereby failing to save the power consumption during the remote control signal receiving period. Moreover, since this device performs the intermittent operation and repeats the normal mode at regular intervals until a remote control signal is received, thereby increasing the average power consumption. The device performs the intermittent operation until a remote control signal is received because the device aims at making the transition from the power saving mode to the normal mode by detecting the input of the remote control signal without using an interrupt terminal.
Patent Document 2 (Japanese Utility Model No. 3065058) discloses a device having two different modes, i.e., the normal mode and the power saving mode in which the power consumption is smaller than that in the normal mode. When making the transition from the power saving mode to the normal mode, the device alternately repeats the normal mode and the power saving mode and then transitions to a continuous normal mode. The average current consumption value during the period in which the normal mode and the power saving mode are alternately repeated is smaller than the current consumption value in the normal mode. The device can gradually increase the average power consumption by gradually increasing the period of the normal mode in the intermittent operation. With this device, the intermittent operation is performed after the remote control signal is received completely. This delays the time at which an operation specified by the remote control signal is started. Another problem is that the power consumption during the remote control signal receiving period cannot be reduced.